Airflow Testing Equipment Arrives

2012 January 20
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The initial testing of the roaster prototype with airflow added went very well. However, all of the observations were strictly visual and subjective. It is important to take accurate measurements to be able to make design decisions. Therefore, we ordered the necessary parts from Dwyer Instruments to do the testing. The primary measurement we need is airspeed or air velocity. This is commonly done using a pitot tube.

Most people have seen a pitot tube at the airport, as it is the way that even the most advanced airliners measure airspeed. On private planes it may be on the wing, airliners usually have several and are near the cockpit.

The pitot tube is pointed into the airflow. It has a hole in the front of the tube and a series of holes on the side. The front hole is used to measure the ram air pressure or total air pressure of the air flowing by. The side holes measure the static air pressure, which is the pressure of the air if it were not moving.

The pitot tube has two pressure taps connected to the holes measuring the two pressures. These are connected via tubing to a manometer.

The manometer measures the difference in pressure and is calibrated to then give the corresponding airspeed. The greater the differential, the greater the airspeed. Obviously with zero airflow the pressure difference is also zero.

We will be using this test setup to measure the airspeed at various point and with various settings in the bowl. This will enable us to quantify both airspeed and airflow. The higher the airflow, the faster heat can be transferred into the coffee beans, so knowing the maximum that maintains proper bean dynamics is very important. Testing shall begin shortly.

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